A process for fabricating semiconductor devices includes several steps for stacking two or more materials on a silicon wafer as a film to be processed and patterning the films with desired patterns. In patterning the films, a photosensitive material called a resist is first stacked on the film to form a resist film and radiation is applied to the prescribed areas of the resist film.
Exposed unit or un-exposed unit of the resist film is removed by a developing treatment to form a resist pattern. The film to be processed is then dry-etched using the resist pattern as a mask.
In this process, ultraviolet rays such as from an ArF excimer laser are used as an exposing source to be exposed to the resist film. Along with an increase in the demand for miniaturization of a large scale integrated circuit (LSI) in the present time, a degree of resolution smaller than the wavelength of the rays used for exposure is required in some cases.
When the resolution decreases to a level less than the wavelength of the rays used, exposure process tolerance such as exposure dose tolerance and focus tolerance may become insufficient. In order to compensate such a shortage of exposure process tolerance, increasing resolution by decreasing the resist film thickness is effective. This method, however, makes it difficult to provide a film with a thickness necessary for etching the film to be processed.
For this reason, a process of first forming a resist under layer film (hereinafter referred to from time to time as “under layer film”) on the film to be processed, then forming an under layer film pattern by transferring a resist pattern onto the under layer film, and transferring that pattern onto the film to be processed using the under layer film pattern as an etching mask is studied. A material having etching resistance is preferably used as the under layer film in such a process.
As such a material for forming an under layer film, a composition containing a resin having a benzene ring which is known to exhibit etching resistance by absorbing energy during etching, in particular, a composition containing a thermosetting phenol novolac, a composition containing a polymer having an acenaphthylene skeleton, and the like have been proposed (see Patent Documents 1 and 2, for example).
As a material for forming an under layer film, a composition containing a specific fullerene compound having an aryl group with 6 to 16 carbon atoms which may contain a phenolic hydroxyl group has also been proposed (see Patent Document 3, for example).    Patent Document 1: JP-A-2001-40293    Patent Document 2: JP-A-2000-143937    Patent Document 3: JP-A-2006-227391